The printing device is provided with a plurality of print heads, each of which has a printing area whose extension in the printing direction fixes a line height, and whose extension transversely to the printing direction fixes a column width. The print heads are arranged in several parallel rows spaced apart from each other. The print heads of different rows are offset transversely to the printing direction in respect to each other.
The term “print direction” in this context means the movement direction of the material to be imprinted relative to the print heads. If printing plates mounted on rotating printing plate cylinders are provided as the material to be imprinted, the print direction extends perpendicularly in respect to the axis of rotation of the printing plate cylinder and tangentially in relation to its surface.
Printing devices of this type are utilized for placing images on printing plates, for example. A coating material, or as the inverse thereof, a solvent for dissolving a coating of the printing plate, can be sprayed on the printing plate by the use of the plurality of print heads.
In order to obtain a printed image of high quality, it is desirable to be able to supply the medium to be applied to the printing plates finely and in an evenly distributed fashion to each area of the printing plate without missing any spots. For this purpose, the print heads must be aligned in relation to each other sufficiently closely and with an accuracy of a few μm. On the other hand, the possible density of packing the print heads close to each other is limited, since they touch each other. It would therefore be desirable to be able to function with as few print heads as possible.
However, conventional print heads do not have any surfaces along which they could be aligned by the use of suitable stops. In order to position such print heads in relation to a desired spot it is therefore necessary to compare the actual position of the print image with the desired position of the print image and to then displace the print heads accordingly.
U.S. Pat. No. 5,719,602 shows an ink jet print head with a multitude of nozzle groups. These nozzle groups are arranged offset in respect to each other.
DE 37 30 844 A1 discloses a matrix ink printer, wherein several print heads, each with several nozzle openings, are arranged offset in relation to each other. In this device, the nozzle openings overlap in relation to the material to be imprinted.
GB 2 349 607 A shows a printing device with a plurality of print heads which are arranged offset in respect to each other. These print heads are arranged inclined in the radial direction in relation to a printing cylinder.
U.S. Pat. No. 4,864,328 shows an ink jet print head with several rows of nozzles. These nozzles are inclined in respect to the printing direction.
U.S. Pat. No. 6,048,08 describes a printing device, whose print heads are stationary during the printing operation, but are positioned in respect to each other for adjustment.
A printing device of the width of a page with several print heads is known from WO 00/64680.
EP 0 998 968 A1 discloses an ink jet for changing a coating on a printing forme.